The present invention relates to apparatuses and methods for implementing mobile communication. More particularly, the present invention relates to a novel private multiplexing cellular network, as well as components therefor, that advantageously offers cellular coverage to private cellular phone sets, i.e., private mobile stations (MS""s), public cellular phone sets, i.e., public mobile stations (MS""s), and hybrid private-public cellular phone sets, i.e., hybrid mobile stations (MS""s) in a seamless manner. In accordance with one aspect of the present invention, the coverage area under control of the private radio subsystem can be used by private MS""s (and hybrid MS""s in certain predefined circumstances) as if it is part of the private network, and by the public MS""s (and hybrid MS""s in certain other predefined circumstances) as if it is part of the public network.
Mobile communication is known in the art. One limited form of mobile communication involves prior art cordless phones. In the prior art cordless phone system, each cordless phone set typically comprises a base unit and a cordless unit. The base unit, typically located inside a residence or a business office, is usually coupled physically by copper wires or fiber optics to the public switched telephone network (PSTN). To uniquely identifies it in the public network, each cordless phone set is specifically associated with a telephone number.
Further, each cordless phone""s base unit is specifically associated with its cordless unit and communicates therewith in a wireless manner. As long as a user of the prior art cordless unit stays within the limited range of the associated base unit (under a quarter mile in most cases due to technical limitations inherent in cordless technology), calls may be made to and from the public network in a wireless manner.
However, the prior art cordless phone has some significant disadvantages. Besides the limited range, the prior art cordless technology is limited in the number of cordless units that a base unit can support. Typically one, no more than two, handset is provided per base unit in the prior art cordless phone. Because of this limitation, a telephone service provider must still run wires, either along telephone poles or in trenches, to each residence or business to enable telephone service, whether or not cordless. Therefore, although the cordless unit appears mobile to the user, the network that is required to implement this service is still essentially a wired telephone network.
Users""demand for mobile communication services, as well as the increasing costs of building and maintaining a wired telephone infrastructure, has turned many service providers to other wireless technologies for answers. Among existing technologies, cellular technology has emerged the clear leader in term of market penetration. In particular, cellular phone systems using a standard known as Global Systems for Mobile Communication (GSM) has steadily gained popularity among service providers as the system of choice for implementing cellular service. The popularity of the GSM standard stems from its robustness and its ability to support a rich set of features such as world-wide roaming, phone mail, data services, supplemental services, and the like. Information regarding the GSM standard is widely available in the public domain, some of which are cited in Appendix B herein.
For illustration purposes, FIG. 1 illustrates a representative prior art public cellular communication system. For illustration purposes, a cellular communication system for use with the Global Systems for Mobile Communication (GSM) protocol is shown in FIG. 1. Referring to FIG. 1, there are shown four mobile station units (MS), also known as cellular handsets, 150, 152, 154, and 156, which communicate to an antenna subsystem 158. As is known to those familiar with the GSM protocol, MS""s 150-156 typically communicate with antenna subsystem 158 via a radio link (RL) protocol. As is known, the radio link (RL) protocol is a LAPD-M protocol at GSM layer 2 and is defined by standard GSM 08.58.
Antenna subsystem 158 couples to transceiver units (TRX) 160 and 162 of base transceiver station (BTS) unit 164 as shown. Each of TRX""s 160-162 outputs bearer data, which may be 8 Kbits per second (Kbps) or 16 Kbps (GSM) time division multiplexed (TDM) data representing, for example, voice conversations, facsimile, digital data, and the like. A TRX also outputs signaling information which is packet information that is forwarded either to antenna subsystem 158 for transmitting to the MS""s or to a base station control function (BCF) 166 for communicating with a base station controller (BSC) or a mobile services switching center (MSC). The mobile services switching center (MSC) will be discussed later herein.
From the GSM point of view, each of MS""s 150-156 contains hardware and software that can handle from its end functions such as radio resources control (RR), mobility management (MM), call control (CC), short message service (SMS), and supplemental services (SS). Base control function (BCF) 166 is coupled to a transcoder-rate adapter unit (TRAU) 168 for switching between either 8 Kbps or 16 Kbps to 64 Kbps TDM data before being passed on to the BSC. A transcoder-rate adapter unit (TRAU) is used for performing rate adaptation, or voice transcoding, between MS units communicating at different rates.
TRAU unit 168 is coupled to an E1 module 170 of BTS unit 164. E1 module 170 represents the means by which BTS unit 164 can communicate with a base station controller (BSC) unit 172. In one embodiment, E1 module 170 represents a 2.048 Mbits signaling wired interface that is channelized into 64K bits channels. BCF 166 represents a CPU module that runs the software to handle provisioning of the TRAU or E1 resources at the request of base station controller (BSC) 172.
In the prior art, BTS unit 164 is essentially a xe2x80x9cdumbxe2x80x9d subsystem that operates responsive to commands from BSC unit 172. For example, when BSC 172 first powers up, it will configure BTS unit 164 via a link 174 by down loading the configuration data across link 174. Link 174 represents the terrestrial link that carries the TDM data between BTS unit 164 and BSC unit 172, typically using an interface known as Abis.
A BSC unit may have multiple E1 modules for communicating with multiple BTS""s. For example, BSC unit 172 is shown having 3 E1 modules 176, 178, or 180 for communicating with 3 or more BTS""s. Furthermore, although BTS 164 shows only two transceiver units 160 and 162 for illustration purposes, it should be understood that a typical BTS unit may have any number of transceiver units.
Functionally speaking, the job of BSC unit 172 is radio resource (RR) control. It manages certain requirements regarding the status and location of the mobile stations and details regarding how to communicate with the mobile stations in the appropriate modulation scheme. In this manner, BSC unit 172 helps to hide this level of detail from any components upstream, e.g., mobile services switching center (MSC) 182 or the public network that is upstream from MSC 182. BSC unit 172 also handles power control. BSC unit 172 directs BTS unit 164 and a transceiver unit therein to increase or decrease its transmission power from a handset to improve transmission quality.
Furthermore, BSC unit 172 also monitors handset communication quality to prepare for power handovers, e.g., when one of the handsets roams among the different areas controlled by different BTS""s. When a hand-over is eminent, BSC unit 172 further initiates the hand-over. The intra-BSC hand-over of the prior art ensures that communication for a single circuit between a given mobile station and MSC unit 182 remains uninterrupted during handover.
BSC unit 172 further includes processor 184 for handling the aforementioned radio resource control (RR), optional TRAU unit 186, and an E1 module 190. E1 module 190 provides the means through which BSC unit 172 can communicate with MSC unit 182.
MSC unit 182 may communicate with any number of BSC unit 172 and includes, among other things, an E1 module 192, a processor 193, and a gateway MSC unit 194. GMSC unit 194 facilitates communication between the cellular communication system of FIG. 1 and the outside world, e.g., the public network. GMSC 194 is coupled to a link 194 for communicating with the public network. As is known, the communication between MSC 182 and the public network may be performed via the E interface.
As is also known to those familiar with the GSM specification, MSC unit 182 further include circuits to handle mobility management (MM), call control (CC) short message service (SMS), and other supplemental services (SS). Optionally, MSC unit 182 performs some radio resource (RR) handling, e.g., inter BSC and inter MSC handovers. Inter BSC occurs when a mobile station roams among the BSC""s. In this case, the radio resource control must be handled by the upstream MSC since a BSC would not know how to hand-over to another BSC when the mobile station roams from a BSC to another BSC.
Although public cellular networks, such as that described in FIG. 1, satisfactorily provide cellular communication capabilities for large urban areas, there are drawbacks. Among the drawbacks discussed in connection with the aforementioned co-pending patent application Ser. No. 08/435,709 are the inefficient backhauling of bearer data channels back to the public MSC for cross-connecting, the indiscriminate use of rate adaptation resources (TRAU) for data channels that do not necessarily require rate adaptation, and the fact that a functional public cellular network may not be a cost-effective solution for geographically remote or applications where the end-user wishes to retain a high degree of control over the addition or removal of users.
In the aforementioned co-pending patent application Ser. No. 08/435,709, there are described methods and apparatuses for implementing various combinations of private cellular networks to address the aforementioned drawbacks of public cellular networks. Referring now to FIG. 2A, there is shown a private cellular network 200, representing a private cellular network of the type disclosed in co-pending patent application Ser. No. 08/435,709. Private cellular network 200 may be coupled to a public network 202 via a connection 204. The coupling between cPBX 200 and public network 202 may be accomplished, in one embodiment, via an E1 interface which may represent a wired or a microwave link.
Private cellular network 200 has sufficient resources to perform switching and communication management among its private MS""s without assistance from the public network. Advantageously, the mobility, roaming, and hand-off capabilities are handled by the resources within private cellular network 200 without the intervention of public network 202. Additional resources or features may thus be added to the private cellular network for the benefit of owners of private MS""s without requiring corresponding changes in the public network.
Within private cellular network 200, shown are a cPBX subsystem 206, a BSC subsystem 208 and BTS subsystem 210, and MS units 212 and 214. As will be discussed later, cPBX subsystem 206, BSC subsystem 208 and BTS subsystem 210 represent the enhanced versions of the respective MSC, BSC and BTS of the prior art.
MS units 212 and 214 represent standard cellular handsets which are GSM standard handsets in the preferred embodiment. MS 212 and 214 communicate with BTS subsystem 210 via an appropriate cellular interface such as the aforementioned radio link (RL) interface. The typical radius of operation between each MS unit and a BTS subsystem is in the range of 2 to 3 Kilometers, which is substantially greater than the 200 meter range typically offered by the prior art wireless wPBX. The additional range offered by the cellular cPBX of FIG. 2A represents a significant advantage because it is difficult, as is well known to those skilled in the communication art, to scale up the distance offered by the prior art wireless bases and cordless handsets due to interference problems inherent in the prior art cordless technology.
Each cPBX subsystem 206 is capable of coupling to more than one BSC subsystem 208. BSC subsystem 208 communicates with cPBX subsystem 206 via link 216 using, for example, an A interface. Similarly, each BSC subsystem 208 is capable of coupling to more than one BTS subsystem 210. BTS subsystem 210 is coupled to BSC subsystem 208 via link 218 utilizing, for example, Abis interface. Further, each BTS subsystem 210 is capable of coupling to a number of MS units, of which only two are shown. In this manner, private cellular network 200 is organized in a hierarchy, the top of which is occupied by cPBX subsystem 206. Depending on system configuration, the cPBX configuration shown in FIG. 2A can handle as few as 7 simultaneous calls up to as many as 1,000 (correlating to up to 10,000 MS""s)
It should be understood that the drawing of FIG. 2A is a functional representation and that the different components of the private cellular network 200 may either be integrated to co-locate at the same location or on a single chassis or dispersed in a wide geographic area to increase the domain of the private network. The ability to configure a physical chassis to perform individual BTS, BSC, or cPBX function, or any combination of these subsystems, represents a unique advantage of the private network disclosed in co-pending patent application Ser. No. 08/435,709.
As will be discussed later, the components of private cellular network 200 are designed such that they can be added or removed from private cellular network 200 in a modular fashion. In this manner, a scalable private cellular network may be realized, whose capabilities may be expanded or shrunk as necessary to fill the need of a particular site.
In the purely private network configuration, each MS unit, e.g., MS units 212 and 214, is registered with and recognizable by cPBX subsystem 206. More particularly, the information associated with each MS unit is registered in a home location registry (HLR) in cPBX subsystem 206. The registration of an MS unit with the HLR registry in cPBX subsystem 206 permits that MS unit to be recognized as a private MS unit and to utilize the resources of private cellular network 200 for cellular communication. For example, a registered MS unit may make calls via BTS subsystem 210, BSC subsystem 208, and cPBX subsystem 206 to a telephone set in public network 202. Alternatively, MS unit 212, being an MS unit that is registered with the HLR registry within cPBX subsystem 206 may make a local call to another MS unit also registered with the HLR registry within cPBX subsystem 206, e.g., MS unit 214 via BTS subsystem 210. When an MS unit is registered with the HLR registry in cPBX 206, it may also receive a call, whether from public network 202 or from another MS unit that is registered with the same HLR registry.
In the purely private network configuration of FIG. 2A, a standard GSM handset that is not registered with the HLR registry within cPBX subsystem 206 is deemed a non-native handset and cannot use the resources of private cellular network 200 to make or receive calls. Further, each of BTS subsystem 210, BSC subsystem 208, and cPBX subsystem 206 is furnished with intelligent cross-connect capability. Consequently, the actual cross-connect that builds the connection between the calling MS unit and the receiving MS unit may be distributed down from cPBX subsystem 206, e.g. to BSC subsystem 208 or BTS subsystem 210. For example, MS units 212 and 214 may be cross-connected at a lower level in the hierarchy, e.g., BTS subsystem 210, instead of at a higher level, e.g., at cPBX subsystem 206. If the call is made between MS units controlled by the same BSC subsystem, e.g., BSC subsystem 208 but different BTS subsystems, the cross-connect switching may be performed at BSC subsystem 208 instead of at cPBX subsystem 206. In this manner, the channels containing the bearer data between MS units do not always have to be backhauled all the way to cPBX subsystem 206.
The intelligence switch capability in the subsystems of private cellular network 200 permits the entire network to handle more traffic by freeing up the bandwidth leading to cPBX subsystem 206 if the required cross-connect between channels carrying bearer data could be performed by a component further down the hierarchy.
In the prior art public cellular systems, e.g., the public cellular system of FIG. 1, cross-connection among call paths is centralized at a central public mobile services switching center. In the prior art, all circuits between the BTS and MSC are rate-adapted, or TRAUed, before the MSC and all MSC cross connect functions are performed at 64 Kbps. This necessitates two TRAUing functions to be performed for calls between two 16 Kbps handsets controlled by the same MSC. In the private network of FIG. 2A, the TRAU is advantageously associated with the gateway to the public network, and need not be employed for calls internal to the network. There is provided TRAU resource within the network, however, to accomplish rate adaptation when necessary, e.g. for calls between a 8 Kbps handset and a 16 Kbps handset.
It is observed that GSM standard MS units in private cellular network 200 transmit and receive data at a predefined rate, say 8 Kbps or 16 Kbps. Since the channels carrying bearer data may be cross-connected by a subsystem within the inventive private cellular network 200 instead of at the public MSC, it is often not necessary to TRAU the bearer data channels for calls between MS units within the private cellular network 200. Consequently, the ability to cross-connect certain calls within the private network without TRAUing advantageously improves communication quality and reduces the computational overhead associated with TRAUing.
FIG. 2B shows in a symbolic format cPBX subsystem 206 of FIG. 2A. Within cPBX subsystem 206, shown are a gateway MSC (GMSC) block 250, a registry 252 which contains both the home location registry (HLR) and the visitor location registry (VLR registry), a private MSC block 254 and a cPBX block 256. GMSC block 250 represents the interface for communicating with the public network, e.g., public network 202 of FIG. 2A. Within GMSC block 250, there is shown a public network interface 258 and a transcoder/rate adapter unit (TRAU) block 260. In one embodiment, public network interface 258 represents a trunk module which has been loaded with the appropriate software for communicating with the public network via standard interfaces such as ISDN, R2, and analog interfaces using inband or common analog signaling.
TRAU block 260 resides in GMSC block 250 to facilitate rate adaptation to build a call between an MS unit of the private cellular network and a telephone set in public network 202 of FIG. 2A. Rate adaptation is necessary because a GSM MS unit and a public network typically transmits and receives data at different rates. It is important to note that the present invention eliminates the TRAUing function whenever possible for calls that are switched within the private cellular network, e.g., between MS units controlled by cPBX subsystem 206. In contrast, prior art public cellular systems automatically provide TRAUing between the prior art BTS and the prior art MSC, either at the BTS, BSC, or between the BSC and the MSC.
In the prior art wireless wPBX, a registry is not necessary since cordless phones are associated with a particular base and do not roam from base to base. In contrast, a registry is preferably provided in the private cellular network of FIG. 2A to provide mobility management of the MS""s. Furthermore, the home location registry (HLR) and visitor location registry (VLR registry) are preferably integrated in registry 252 of the private cellular network.
Registry 252 of private cellular network 200 of FIG. 2B serves, among others, to keep track of MS units that are authorized to use the resources of the private cellular network, the subscriber data such as names, unique identification information such as is kept in Subscriber Identification Module (SIM) for GSM handsets, telephone numbers associated with the MS units, and the like. Subscriber information is kept track of because private cellular network 200 must keep track of the MS units controlled by it as well as the subscribers on its network.
PBX block 256 handles supplemental services (SS) that may be offered by private cellular network 200. Furthermore, PBX block 256 handles the call control (CC) function, which includes the ability to intelligently understand the destination intended for the telephone number dialed. In one embodiment, the destination intended for the number dialed is determined in accordance to a numbering system. By way of example, extensions 2000 to 6000 may indicate a destination MS unit inside private cellular network 200, while other numbers dialed may indicate calls that must be routed to telephone sets in the public network. PBX block 256 may also contain circuits for performing functions typically expected of a PBX system such as call forwarding, call transfer, and the like.
Private MSC block 254 handles mobility management (MM) and with the help of the PBX (256) radio resource (RR) management. The PBX 256 handles call processing (CC) and Supplemental Services (SS) via the MM session and assists with RR by forwarding calls between cPBX""s for handsets that have roamed into the coverage area of other cPBX""s or need to be handed over to another cPBX.
Switching decisions are made by the PBX 256. However, in some applications, private MSC 254 may listen to messages sent across the MM session to decide whether or not it should act as a BSC. When acting as a BSC, the PBX function is bypassed, the circuit cross connect function to public MSC is made by the private MSC function.
The intelligence within the private PBX block 256 may decide that switching may be more efficiently performed at a BSC or BTS further down the hierarchy. In this case, there is a signaling connection between the MS units and the cPBX for CC and SS control via the private MSC MM session. However, the switched voice/data path for the call will not traverse the cPBX, but will be cross connected by the BSC""s and/or BTS""s further down the hierarchy.
Although the strictly private cellular network represents cost-effective and efficient cellular solutions for some markets, it has been recognized that strictly private cellular systems that do not make its radio subsystem resources to public MS""s, i.e., MS units not specifically registered with the home location registry of the private network, has some drawbacks in certain applications. For example, some private cellular networks may utilize the same cellular frequency for operation as the public network. In this case, the fact that public MS""s cannot utilize the radio resources of the private cellular network to make and receive calls while roaming within the coverage area of the private cellular network means that there is a lapse or xe2x80x9cholexe2x80x9d in coverage, from the perspective of the public MS users, while roaming.
In other cases, the private cellular networks may be employed as temporary cellular networks to offer cellular service to geographical locations too remote or economically unrewarding to warrant the implementation of a full-scale public cellular network. In these cases, it may be desirable to build into the private cellular network a migration path such that when the public cellular network eventually grows and reaches the locations currently serviced by the private cellular network, the integration of the private radio subsystem resources into the public network to offer cellular service to public cellular system customers would be gradual and seamless for both the current private cellular system customers (who own private MS""s and are registered with the private HLR), and the public cellular system customers (who own public MS""s and are not known to the private HLR). Such gradual and seamless migration permits the use of the private radio subsystems by both the private and public MS""s to originate and receive cellular services as the public network coverage area grows and encompasses the coverage area under control of the private radio subsystem. Advantageously, the private MS""s do not have to be replaced if and when the public network coverage area reaches the private network coverage area, and the public MS""s do not have to suffer a lapse of coverage while being within the private network coverage area.
These and other highly desirable features that overcome the disadvantages associated with traditional cordless phone systems as well as strictly private or public cellular systems are realized by the novel private multiplexing cellular network, which is described in details in the text of this specification and its drawings.
The present invention relates, in one embodiment, to a private multiplexing cellular network that advantageously facilitates cellular communication for private MS""s. Further, the inventive private multiplexing cellular network allows the public MSC""s to employ its private radio resources to facilitate cellular communication for public MS""s in a seamless manner while those public MS""s are within the coverage area of the private multiplexing cellular network.
Advantageously, the implementation of a private network does not thereby result in a lapse or xe2x80x9cholexe2x80x9d in cellular coverage for users of public MS""s. In fact, public MS users can rely on the private multiplexing cellular network to provide radio subsystem resources for cellular communication in areas where the public network coverage has yet to reach. Additionally, the seamless manner with which public MS""s employ the private radio subsystem resources to make and receive calls represents an efficient built-in migration path for integrating the private network into the public network in the future. For private MS users, all advantages associated with a private cellular network still apply.
In accordance with one aspect of the present invention, at least one BSC of the private multiplexing cellular network is coupled to a multiplexing circuit. The multiplexing circuit is in turned coupled to two A-interfaces: a private A-interface for communicating with the private MSC and a public A-interface for communicating with the public MSC. Via the multiplexing circuit, calls from within the private multiplexing cellular network coverage area may be built, in a multiplexed manner, to either the public MSC or the private MSC. Likewise, calls that arrive at the private network coverage area via either MSC may be routed, via the multiplexing circuit, to the destination MS within the private network coverage area.
In accordance with yet another aspect of the invention, there is provided within the multiplexing circuit intelligence for deciding whether the public A-interface or the private A-interface should be employed for servicing a service request received from either the MS""s within the private multiplexing cellular network coverage area or from one of the MSC""s.
In accordance with yet another embodiment of the invention, the private multiplexing cellular network facilitates cellular communication for a class of novel mobile stations, known herein as hybrid mobile stations (MS). A hybrid mobile station has two telephone numbers associated with its Subscriber Identification Module (SIM): a public telephone number which is known to the public network, and a private telephone number, which is known to the private multiplexing cellular network. Since a hybrid MS is known to both networks, albeit via different telephone numbers, a hybrid MS may be operated within both networks. Either of the public or private telephone numbers may be dialed, and the intelligence within the multiplexing circuit decides whether the public MSC or the private MSC should handle the call depending on which number is dialed.
These and other features of the present invention will be presented in more detail in the following specification of the invention, the figures, and the appended claims.